The present invention relates to a forcible commutation type power control or conversion apparatus using controlled electric valve.
In inverters or DC power controllers, it is common to switch at least one pair of controlled rectifier elements connected in series-parallel combination (bridge or half-bridge connection). Diverse methods for commutating such connected components have been known, with one of the prior arts close to the invention being Japanese Patent Publication No. 24447/'67. In the prior art, the controlled rectifier bridge (controlled electric valve bridge) and the rectifier bridge (electric valve bridge) are direct-coupled in anti-parallel combination. A reverse bias impulse current is applied to both the bridges thereby to simultaneously turn off the controlled rectifier element. This method is defective in that the rise rate (turn-off dv/dt) of the reapplied forward voltage immediately after the extinction, is remarkably high. Furthermore, the reverse bias impulse current flows into a plurality of rectifier elements branches. The reduction of the forward currents to be commutated of the controlled rectifier elements to be turned off, is considerably impeded by the wiring inductances or anode reactors (for example, reactors for restricting the turn-on di/dt or saturable reactors for restricting dv/dt). In other words, the commutation or reverse biasing are difficult. Particularly in the case of large current units, a slight wiring inductance considerably increases the desired commutation impulse current.
In the light of the just-mentioned disadvantages of the prior art apparatus, the present invention has an object to provide an AC power supply apparatus of easy-switching forced commutation type, having a current-source like output characteristic.